How Many Reps?

First of all, there is no definite answer to this question. It depends on the muscle being worked out, the person, and the goal. Lets look at the extremes first. A powerlifter is interested in a one-rep maximum lift and the goal of their training is to do just one rep with as much weight as possible. On the other extreme is a marathon runner whose goals is to do about 45,000 mini-lunges as quickly as possible.

The one thing I would say is that it is important to vary the number of reps you do at least on a monthly basis. The body is excellent at adapting. If you only do high rep with low weight, the body will quickly adapt to that and you won't make any more gains. If you only do heavy lifting with single reps, your body will quickly adapt to that too. For those of you hard core power-lifters out there who scoff at this idea, try this. Rather than doing a chest workout with high weights and single reps, do my workout which basically just consists of a hour of pushups. I can guarantee you that even if you can bench 405lbs, if you do a hour of high rep pushups your chest will be destroyed the next day. Doing heavy weights with a single rep max or very few reps (less than 5) might be good for developing strength but it sure take a toll on the joints. Personally, I try to limit heavy lifting like this to two week periods done twice a year.